As a current sensor attached to an electric wire to measure a current supplied to the electric wire, for instance, below-described current sensors have been hitherto known (for instance, see patent literatures 1 to 3).
The current sensor described in the patent literature 1 includes a case in which electrical parts are accommodated and a cover. The case is formed in a cylindrical shape with a bottom including a bottom wall of a doughnut form in a plan and peripheral walls standing from an inner edge and an outer edge of the bottom wall. The cover is attached to the case so as to cover an opening of the case therewith. In the cover, a tubular guide part is provided that is allowed to pass through the center part of the case and allows an electric wire to pass through an inner part thereof. The inside diameter of the tubular guide part is formed to be slightly larger than the outside diameter of the electric wire. The electric wire is allowed to pass through the tubular guide part without a backlash, so that the deterioration of a measurement accuracy of the current sensor due to the backlash of the electric wire can be prevented.
Further, the current sensor described in the patent literature 2 includes a case in which electrical parts are accommodated and a fastening unit. The case is formed in a box shape. In the case, a through hole is formed that allows an electric wire to pass through. The fastening unit fastens the electric wire allowed to pass through the through hole to the case, and includes, for instance, a fixed mount part protruding from the outer edge of the through hole to mount the electric wire on an upper surface thereof and a fastening band that fastens the electric wire mounted on the fixed mount part to the fixed mount part. Since the electric wire is allowed to pass through the through hole without a backlash by the fastening unit, the deterioration of a measurement accuracy of the current sensor due to the backlash of the electric wire can be prevented.
A clamp shaped current sensor described in the patent literature 3 includes a pair of sensor heads, one side flat plate shaped partition wall part provided in one sensor head and the other side U-shaped groove type partition wall part provided in the other sensor head. When the pair of the sensor heads are overlapped together, a clamp measurement window having an inside diameter substantially equal to an outside diameter of an electric wire is formed by the one side partition wall and the other side partition wall to allow the electric wire to pass through the clamp measurement window. Since the electric wire is allowed to pass through the clamp measurement window without a backlash, the deterioration of a measurement accuracy of the current sensor due to the backlash of the electric wire can be prevented.    [patent literature 1] JP-A-2003-121476    [patent literature 2] JP-A-2006-78316    [patent literature 3] JP-A2005-37284
However, in the current sensors described in the patent literatures 1 to 3, a problem arises that the current sensors hardly meet the electric wires having different outside diameters. That is, the inside diameter of the tubular guide part needs to be changed, the inside diameter of the through hole and the length of the fastening band need to be changed or the inside diameter of the clamp measurement window needs to be changed so as to meet the outside diameter of the electric wire.
Further, in the current sensors described in the patent literatures 1 and 2, after the current sensor is attached to the electric wire, are carried out works that a terminal fitting is attached to the terminal of the electric wire or the electric wire is arranged. However, during these works, a problem arises that the current sensor collides with a periphery to be failed or the current sensor interferes with the work to deteriorate the efficiency of the work. Further, when the current sensor is brought into a failure after the electric wire is arranged in a prescribed wiring passage, a problem arises that a great labor and time are necessary for replacing the current sensor by a new current sensor. As one of countermeasures for the above-described problems, a method is considered that the current sensor is attached to the electric wire after the terminal fitting is attached to the electric wire. However, when the terminal fitting is previously attached to the electric wire, since the terminal fitting needs to pass through the tubular guide part or the through hole, the inside diameter of the tubular guide part of the through hole is inconveniently enlarged to make the current sensor large.
It is an object of the present invention to solve the above-described problems. Namely, it is an object of the present invention to provide a current sensor that can be simply attached to electric wires having different outside diameters without a backlash.